Terms
One invoice can be saved without an account. Pro is £12 a month, billed by Stripe, and can be cancelled. Customer payments made with the bank details, PayPal, or Stripe link on an invoice are between you and your customer. This site does not hold that money.
The sample firm in the book, Hearth & Tenon, is fictional. Replace it with your own company, tax number, and bank details before you send a real bill. The calculators are workshop estimates, not a CIS filing or a building-control approval.